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New idea for simplifying Higgs analysis

If the long-expected Higgs particle is indeed discovered by the LHC then how will we know for certain that it possesses the characteristics predicted by the Standard Model of elementary particles? Speculations about extensions of the Standard Model, such as supersymmetrical extensions, often contain several Higgs bosons. These not only differ in mass but also in their behaviour under spatial reflections, for example. Measurements of complex angular distributions of the decay products could be used to determine that behaviour. However, a simpler way could be to examine the momentum distribution of the Higgs-like particle. This new idea has been proposed in an article published this week by the renowned journal Physical Review Letters.

At the LHC, protons are accelerated to an energy of 3.5 teraelectron volts and then made to collide in the hope of producing the long-expected Higgs particle. This particle is vitally important in the Standard Model, as it ensures that other elementary particles, such as electrons and quarks, acquire mass. The Standard Model Higgs particle is a spin-0 particle that remains invariant under spatial reflections. Experimental testing of this characteristic property becomes far simpler with this new approach.

The new idea utilises the fact that the fusion of two gluons in particular produces a Higgs particle. Gluons are the force particles - let's say the photons - of the strong nuclear interaction. The proton-proton collisions at the LHC are mainly gluon-gluon collisions. Therefore the LHC is sometimes called a 'gluon collider' as well. These gluons can also be polarised even if the protons are not. So in a certain sense the LHC is also a 'polarised gluon collider'. The degree of polarisation is not yet known but this might well influence the momentum distribution of the Higgs particle. It ensures such a characteristic distribution that the behaviour of the Higgs particle under spatial reflections becomes apparent. In view of the many complications involved in measuring heavy particles with a brief existence, such as the Higgs particle, every simplification is extremely welcome.

This research was carried out under the leadership of Prof. Daniël Boer (KVI, University of Groningen) in collaboration with the VU University Amsterdam and the universities of Tübingen and Cagliari within FOM programme nr. 104 'Theoretical particle physics in the era of the LHC'.

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A possible transversal (perpendicular to the proton beams) momentum distribution for a scalar Standard Model Higgs (left) and a pseudoscalar Higgs from, for example, supersymmetric extensions of the Standard Model. The darker areas indicate a high density.Â